Fix hover tooltip for layout containers

[optozorax]

I have found that ui.horizontal(...).response.on_hover_text(...) doesn't work, although documentation says otherwise:

The returned Response will only have checked for mouse hover but can be used for tooltips (on_hover_text). It also contains the Rect used by the horizontal layout.The returned Response will only have checked for mouse hover but can be used for tooltips (on_hover_text). It also contains the Rect used by the horizontal layout.

So I added fix to this into tooltip, but this looks like a hack, and I don't know a better place to do so. Do you have a better idea?

This PR is split into two commits: first commit adds test, and you can see wrong behaviour in the image. Second commit fixes this and also regenerates the image and you can now see tooltip.

I have used LLM to help me with this PR (codex). And I retained LLM comment, because such hacks should have some comments, and it seems ok to me.

[github-actions]

Preview available at https://egui-pr-preview.github.io/pr/7909-reproduce-horizontal-tooltip-regression-from-main
Note that it might take a couple seconds for the update to show up after the preview_build workflow has completed.

View snapshot changes at kitdiff

[optozorax]

Hi, @emilk , can you please take a look at this PR?

[optozorax]

@emilk done!

[emilk]

Hum - I wanted to test that the tooltip for B pops up, but in this case I think we just hit the logic of "keep the previous tooltip open"? I think this needs to be a separate test then